For the long-wave infrared camera which has a temperature sensitivity less than 10 mK, it is an important work of testing its noise equivalent temperature difference(NETD) with high accuracy. Firstly, the "black body direct testing method" was chosen based on the principle of shortening the standard radiation transfer link and reducing the error terms after comparing different testing methods; Secondly, based on the theoretical noise model of the long-wave infrared camera, the testing noise data was analyzed at different temperatures, the noise correction method was proposed for reducing the testing error caused by the instability of environment. Finally, the uncertainty of testing results was analyzed based on the NETD calculation formula and analysis theory of uncertainty. The result shows that the testing device and methods are satisfied for the testing requirement of ultra-high sensitive long-wave infrared camera, the testing uncertainty is 7.7%.